1. Field of the Invention
The present invention relates to screen-printing apparatus and, more specifically, to a screen-printing apparatus having pneumatically operated clamping devices for holding the edge of a rigid frame of a printing screen in order to permit faster and easier replacements of print screens.
2. Description of Related Art
Various types of manually operated screen-printing apparatus are known in the prior art. One commonly used type of construction is known as the Harco screen-printing machine made by Brown Manufacturing Company, as described in U.S. Pat. No. 4,809,604, issued to Harpold on Mar. 7, 1989, which is incorporated herein by reference.
The Harco machine typically includes four separate head units, each head unit being capable of holding one print screen by clamping onto an edge of the rigid frame surrounding the screen that contains the indicia. Each of the four heads is mounted onto a carousel that can be rotated to align any one of the four print screens with a textile article, such as a T-shirt or jersey, placed on a platen. Ink is then applied to the surface of the screen, passing through the unmasked portion of the screen to the exposed and aligned surface of the textile article. In addition to the typical four-head apparatus, similar manually operated apparatus have been equipped with one, two or six heads as well. In this and other similar devices, the print screens are generally clamped in place along an edge of the screen frame by hand using threaded knobs. Mounting and remounting of screens is time-consuming and labor-intensive, especially when multiple print screens having different indicia are required.
Improvements in screen-printing apparatus are known in the relevant art. Pneumatic or hydraulic devices for raising and lowering the print screen, for positioning the workpiece, and for stretching the screen on a frame are a few of the improvements disclosed in the related art.
U.S. Pat. No. 4,022,156, issued to Esterline on May 10, 1977, teaches a hydraulically operated work holder in which the device opens or closes a frame. U.S. Pat. No. 4,079,671, issued to Dubuit on Mar. 21, 1978, teaches a screen-printing machine for printing onto an article placed on a cylindrical support using a hydraulically or pneumatically actuated squeegee.
U.S. Pat. No. 4,442,772, issued to Bubley on Apr. 17, 1984, teaches a screen tensioning apparatus using a pneumatic tensioning device. U.S. Pat. No. 4,696,228, issued to David et al. on Sep. 29, 1987, describes a cantilevered support frame to hold a screen that includes a pneumatically actuated bladder.
U.S. Pat. No. 4,771,687, issued to Daunheimer on Sep. 20, 1988, teaches a pneumatically operated screen-printing apparatus for printing nonplanar workpieces in which the pneumatic device moves the screen into place on the workpiece. U.S. Pat. No. 4,829,894, issued to Gardner on May 16, 1989, teaches a balloon printing machine having a pneumatically operated squeegee.
U.S. Pat. No. 4,974,508, issued to Anderson et al. on Dec. 4, 1990, teaches a four-head manually operated screen-printing apparatus. U.S. Pat. No. 5,197,388, issued to Keast et al. on Mar. 30, 1993, teaches a clamping apparatus for use in the screen of curved articles wherein the curved workpiece is held in place by a spring biased clamp.
U.S. Pat. No. 5,235,908, issued to Froelicher et al. on Aug. 17, 1993, teaches a screen fabric stretching apparatus having pneumatic stretching components. U.S. Pat. No. 5,309,831, issued to Fuqua et al. on May 10, 1994, teaches a rotatable multicolor screen-printing apparatus having a powered squeegee device.
U.S. Pat. No. 5,454,307, issued to Chen on Oct. 3, 1995, teaches an apparatus for screen-printing shoe soles including pneumatically actuated clamping members. U.S. Pat. No. 5,740,732, issued to Karlyn et al. on Apr. 21, 1998, teaches an apparatus for simultaneously manufacturing a plurality of annularly shaped screen frames.
U.S. Pat. No. 5,913,263, issued to Hruska on Jun. 22, 1999, teaches a device using pneumatic devices to stretch printing screens.
None of the above inventions and patents, taken either singly or in combination, is seen to describe a manually operated screen-printing apparatus having a pneumatic clamping device for quickly and easily holding or releasing a printing screen as claimed.
The present invention is a screen-printing apparatus in which print screens are held in place by a pneumatically actuated clamping device. The screen-printing apparatus may includes at least one screen-holding head, each head having clamped to it an edge of a print screen frame. The apparatus uses switch actuated pneumatic cylinders to cooperatively engage or disengage clamps holding an edge of a print screen frame to the screen-printing apparatus.
When a complete set of jerseys for use by an entire sports team, e.g., for hockey or football, is produced, multiple screens having a variety of indicia are needed, necessitating frequent changing of the print screen during production. The screen=printing apparatus of the present invention reduces the time needed to interchange the print screens during production.
Accordingly, it is a principal object of the invention to provide a screen-printing apparatus in which an edge of a print screen is held in place by a pneumatically operated clamping device.
It is another object of the invention provide an apparatus including a plurality of print screen holding heads mounted on a carousel, each print head having pneumatic clamping devices.
It is a further object of the invention to provide an air distribution system that is centrally mounted within a carousel supporting a plurality of print screen holding heads, thereby allowing the carousel to rotate freely about the air supply without entangling the air supply tubes supplying each clamping device.
Still another object of the invention is to provide a screen-printing apparatus in which each print screen holding head includes a pair of pneumatic cylinders operated in tandem.
It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.